A versatile intermediate for a variety of 2-fluoro substituted benzenes is 2-fluorobenzonitrile. For example, hydrolysis of 2-fluorobenzonitrile leads to 2-fluorobenzoic acid or 2-fluorobenzamide while reduction of 2-fluorobenzonitrile leads to 2-fluorobenzylamine. Also, the reaction of 2-fluorobenzonitrile with organometallic reagents results in various 2-fluorophenyl ketones.
Most processes for the preparation of 2-fluorobenzonitrile fall into one of two categories. In the first type, a 2-fluoro substituted benzene derivative is transformed into the cyano compound by way of a functional group interconversion. For example, U.S. Pat. No. 4,124,631 teaches that 2-fluorotoluene would be converted by ammoxidation into 2-fluorobenzonitrile; disadvantages of this method are that a reaction temperature of 300.degree. to 650.degree. C. is required and 2-fluorotoluene is an expensive starting material. As another example, CA 71:80992d(1969) teaches that 2-fluorobenzoic acid would react with a nitrile to form 2-fluorobenzonitrile; one disadvantage of this method is that 2-fluorobenzoic acid is an expensive starting material.
In the other type, 2-chlorobenzonitrile is converted with potassium fluoride to 2-fluorobenzonitrile in a variety of solvents and with or without additives such as phase transfer catalysts. One disadvantage of this method is that 2-chlorobenzonitrile is an expensive starting material. CA 99:87839w(1983) teaches that 2-chlorobenzonitrile is converted with potassium fluoride in 1,3-dimethyl-2-imidazolidinone to 2-fluorobenzonitrile. CA 105:114707c(1986) teaches that 2-chlorobenzonitrile is mixed with potassium fluoride in tetramethylene sulfone and refluxed for 30 hours to form 2-fluorobenzonitrile; this method is particularly disadvantageous because the reaction time is so long. CA 109:92451t(1988) teaches refluxing 2-chlorobenzonitrile and potassium fluoride in sulfolane in the presence of meta-C.sub.6 H.sub.4 (NO.sub.2).sub.2 for 24 hours to give 2-fluorobenzonitrile.
N. Yazawa et al., "Tetraphenylphosphonium Bromide Catalyzed Fluorodenitrations and Fluorodesulfonylations. Efficient Syntheses of m-Fluoroaromatic Compounds," CHEMISTRY LETTERS. 2213 (1989) teaches the reaction of 3-nitrobenzonitrile with tetraphenylphosphonium bromide and phthaloyl chloride to form 3-fluorobenzonitrile.
It is desired to have a process for the preparation of 2-fluorobenzonitrile wherein the starting material is inexpensive.